This invention relates to lasers and, more particularly, to broadly tunable chromium-doped beryllium aluminate lasers. Further, the invention also relates to improved chromium-doped beryllium aluminate laser rods employed in such lasers and the method of manufacturing the improved laser rods.
More particularly, the invention relates to an improved laser rod and method of manufacturing such a laser rod of the type employed in the laser discussed in U.S. Pat. No. 4,272,733, whose disclosure is specifically incorporated by reference herein.
In that patent, laser materials are described as being materials which depend on their ability to absorb energy in such a way that more atoms (or molecules) are excited into a higher energy level than are in the terminal state, rendering the material capable of "stimulated" emission. If light of the appropriate wavelength is incident on such excited material, it will emit additional light having the same wavelength, phase and direction as the incident light. This additional light, by augmenting the intensity of the incident light, demonstrates light amplification. This is a well-known principle demonstrated as early as 1960 using ruby, a crystalline solid system.
This invention relates to what are generally known as host-type lasers which employ a dopant ion incorporated in dilute concentration in a solid host as the laser-active component. The invention disclosed in U.S. Pat. No. 4,272,733 is directed to such a host-type laser wherein the solid host is chromium-doped beryllium aluminate, and to which the present invention is directed and is an improvement thereover.
More specifically, the present invention is directed to an improvement in an "alexandrite" laser which, as used in this specification and as well known in the art, is intended to mean trivalent chromium-doped beryllium aluminate (BeAl.sub.2 O.sub.4 :Cr.sup.3+) of the chrysoberyl structure. Typically, alexandrite serves as a host to provide a broadly wavelength-tunable laser which is made up of a laser medium comprising a single crystal of alexandrite having a trivalent chromium doping concentration typically from about 0.002 to 10 atom percent with respect to aluminum sites, means for exciting the laser medium to emit coherent radiation and tuning means for tuning the coherent radiation in a spectral range from red to infrared.
A problem with alexandrite however is that when a crystal of alexandrite which is machined into an alexandrite laser rod is submitted to such a machining procedure, physical stresses are induced, i.e. mechanical stresses, which affect the optical quality on output of the laser rod. More specifically, typically these alexandrite rods are manufactured by conventional core drilling, thereafter grinding and polishing operations. The grinding operation itself induces mechanical stresses on the crystalline structure and this is what ultimately results in deteriorated optical quality upon output. In accordance with the invention, in part a rod is provided which is treated in a manner which corrects and relaxes these induced mechanical stresses or stressing of the single crystalline structure.